Anatomical Study On The Postnatal Development Of The Gastrointestinal Tract In Male Rabbits

Abstract

1. A gross anatomical, histological and ultrastrctural study has been conducted on the GIT in 50 male rabbits (Lepus Cunculus) of different ages. The ages varied between 0-day 30 days. 2. The advancing age is a major factor in the increase of the body weight, crown rump length, fore limb length and GIT weight, length and volume, but there was a decrease in some of these parameters at the age of 30 days. This decrease may be due to the effect of weaning. 3. The location of the stomach in all age groups is similar to that of the adult. 4. The histology (in 32 animals) and ultrastrcture (in18 animals) of the mucosa of the fundic region, proximal and distal small intestines, and caecum and colon were investagated in rabbits of different ages. 5. The histological measurements of the thickness of the fundic mucosa and length of the pits and length and width of the villi of the proximal and distal small intestines were studied in 18 rabbits of different ages. 6. The mucopolysaccharide and glycogen were examined in the fundic region of the stomach, proximal and distal small intestine and colon in rabbits of different age. 7. The mucosa of the fundic region has different shapes in the different age groups, specially in the length of the folds and the depth of the pits. 8. In the fundic region of the stomach, the histology of the surface epithelial cells and parietal cells and chief cells of the gastric glands were studied. The muscularis mucosa was arranged into inner circular layer at 0-day of age, but an additional outer longitudinal layer appeared in older age groups. 9. The age also has an effect on the shape and length of the intestinal villi of the small intestine and the crypts of the large intestine. The mucosa of the small intestine showed simple striated columnar epithelial cells and prominent goblet cells. The crypts opened adjacent to the bases of the villi as simple, branched, tubular invaginations. 10. In the stomach fundic region, the epithelial cells contained apical microvilli, smooth and rough endoplasmic reticulum, free ribosomes, elongated nucleus, secretary granules, mitochondria and electron dense material. Cells with round secretary granules of different size concentrated beneath and lateral to the nucleus were observed in all age groups may be endocrine cells. 11. The mucosa of the small intestine was covered by columnar cells that contained apical microvilli, oval nucleus, dilated cisternae of rough endoplasmic reticulum, Golgi apparatus, vacuoles and material with electron density in all age groups. 12. In the small intestine, the crypts showed epithelial cells with dilated intercellular spaces and contained apical microvilli, mitochondria, material with electron density, rough endoplasmic reticulum and elongated nucleus. There are cells containing spherical secretary granules different in size above the nucleus and cells of polymorphic secretary granules of different sizes beneath and lateral to the nucleus were observed. 13. The mucosa of the large intestine was composed of crypts with villar shape at 0-day of age and the length of the crypts decreased with advancing age. The crypts were lined by striated epithelial cells. Goblet cells were prominent. 14.The absorptive columnar cells had apical microvilli and contained vacoules of different size, ovoid to elongated nucleus, mitochondria, rough endoplasmic reticulum and lateral membranous interdigitations. Cells with polymorphic secretary granules were noticed. 15. Varing degrees of positive reaction to PAS diastase resistant material and diastase-digested material was clearly seen in the stomach fundic region, proximal, and distal small intestine and colon in rabbits of different ages.